An Introduction to Interfaces and Colloids

The following sections are included:

• PREFACE

• CONTENTS

The following sections are included:

• Interfaces

• Colloids

• The bridge to nanoscience
  • What is “nanoscience?”
  • Nanostructures and assemblies
  • Generic nanoscience
  • New tools of generic nanoscience
  • The plan

The following sections are included:

• Fluid interfaces: Young's membrane model
  • The thinness of interfaces
  • Definition of surface tension

• The surface tension of liquids
  • Pure liquids
  • Temperature dependence of surface tension
  • Surface tension of solutions

• Intermolecular forces and the origin of surface tension
  • Van der Waals forces
  • Surface tension as “unbalanced” intermolecular forces; the Hamaker constant
  • Pressure deficit in the interfacial layer; Bakker's equation
  • Components of the surface tension

• Interfacial tension
  • Experimental interfacial tension
  • Combining rules for interfacial tension

• Dynamic surface tension

• Capillary hydrostatics: the Young-Laplace Equation
  • Capillary pressure: pressure jump across a curved fluid interface
  • The curvature of a surface
  • Derivation of the Young-Laplace equation
  • Boundary conditions for the Young-Laplace equation

• Some solutions to the Young-Laplace equation
  • Cylindrical surfaces; meniscus against a flat plate
  • Axisymmetric and other surfaces
  • Nondimensionalization of the Young-Laplace equation; the Bond Number
  • Saddle-shaped surfaces

• The measurement of surface and interfacial tension
  • Geometric vs. force methods
  • Capillary rise
  • Sessile drop and pendant drop
  • Du Noüy ring detachment
  • Wilhelmy slide
  • Langmuir film balance
  • Drop weight (or volume)
  • Maximum bubble pressure and dynamic surface tension
  • The pulsating bubble “surfactometer”
  • Elliptical (vibrating) jet
  • Contracting circular jet
  • Problems with interfacial tension measurement
  • Spinning drop method

• Forces on solids in contact with liquids: capillary interactions
  • Liquid bridges
  • Shared menisci

• Effect of curvature on the equilibrium properties of bulk liquids: the Kelvin Effect
  • The vapor pressure of small droplets and liquids in pores
  • The effect of curvature on boiling point
  • Capillary condensation
  • Nucleation

• Thin liquid films
  • Disjoining pressure and its measurement
  • The molecular origin of disjoining pressure
  • The disjoining pressure isotherm
  • The augmented Young-Laplace equation

• Some fun things to do: Experiments and demonstrations for Chapter 2
  • The thinness of clean interfaces
  • Soap bubbles and films
  • Liquid bridges
  • Shared menisci

The following sections are included:

• The thermodynamics of simple bulk systems
  • Thermodynamic concepts
  • The simple compressible system

• The simple capillary system
  • The work of extension
  • Heat effects; abstract properties; definition of boundary tension

• Extension to fluid-solid interfacial systems
  • The work of area extension in fluid-solid systems
  • Compound interfacial systems; Young's equation

• Multicomponent interfacial systems
  • The Gibbs dividing surface and adsorption
  • Immiscible interfacial systems
  • The measurement of adsorption
  • The phase rule; descriptive equations for binary interfacial systems

• The Gibbs adsorption equation

• Surface tension of solutions
  • Ideal-dilute capillary systems
  • Moderately dilute capillary systems

• Surface active agents (surfactants) and their solutions
  • The structure of different types of surface active agents
    • Anionic surfactants
    • Cationic surfactants
    • Nonionic surfactants
    • Amphoteric surfactants
    • Zwitterionic surfactants
  • Solutions of non-electrolyte surfactants
  • Solutions of electrolyte surfactants

• Self-assembly of surfactant monomers in solution
  • Formation of micelles: critical micelle concentration (CMC)
  • Solubilization

• Micelle morphology, other self-assembled structures, and concentrated surfactant solutions
  • Micellar shape and the Critical Packing Parameter (CPP)
  • Beyond micelles: other self-assembled structures
  • Concentrated surfactant solutions; liquid crystalline mesophases
  • Kinetics of micellization and other self-assembly processes

• Dynamic surface tension of surfactant solutions
  • Diffusion-controlled adsorption
  • Finite adsorption-desorption kinetics

• Insoluble (Langmuir) monolayers
  • Formation of monolayers by spontaneous spreading
  • Hydrodynamic consequences of monolayers: Gibbs elasticity
  • π-A isotherms of insoluble monolayers
  • Langmuir-Blodgett films
  • Transport properties of monolayers

• The thermodynamics of fluid-solid interfacial systems revisited
  • The concept of interfacial energy and its measurement in fluid-solid systems
  • Adsorption of non-polymeric molecules at the solid-liquid interface
  • Experimental measurement of small molecule solid-liquid adsorption
  • Adsorption of polymers at the solid-liquid interface

• Some fun things to do: Experiments and demonstrations for Chapter 3
  • The work of surface area extension
  • Surface tension reduction with surfactant
  • CMC determination by dye titration
  • Insoluble monolayers
  • Adsorption from solution by activated carbon

The following sections are included:

• Wettability and the contact angle: Young's Equation
  • Importance of wetting; definition of contact angle
  • Young's equation revisited; classification of wetting and contact angle values

• Contact angle hysteresis
  • Origins of hysteresis: roughness and heterogeneity
  • Complexity of real surfaces: texture and scale
  • Wenzel equation for rough surfaces
  • Cassie-Baxter analysis of heterogeneous surfaces; composite surfaces and ultra-hydrophobicity
  • The dynamic contact angle; Tanner's Law

• Methods for measuring the contact angle
  • Optical or profile methods: contact angle goniometry
  • Force methods: contact angle tensiometry
  • Dynamic contact angle measurement

• Relation of wetting behavior to surface chemical constitution
  • Zisman plots; the critical surface tension
  • The wettability series
  • Estimates of surface energies from contact angle data or vice versa
  • Thermodynamics of solid-liquid contact: work of adhesion, work of wetting and work of spreading; the Young-Dupré equation
  • The promotion or retardation of wetting: practical strategies

• Spreading of liquids on solid surfaces
  • Criteria for spontaneous spreading; spreading morphology
  • Temperature effects of wetting; heats of immersion and wetting transitions
  • The kinetics of spreading on smooth surfaces
  • Spreading agents; superspreaders

• The relationship of wetting and spreading behavior to adhesion
  • Definition of adhesion; adhesion mechanisms
  • The “Laws of Molecular Adhesion”
  • “Practical adhesion” vs. “thermodynamic adhesion”
  • The importance of wetting (contact angle) to practical adhesion
  • The optimization of thermodynamic contact adhesion
  • Acid-base effects in adhesion
  • Contact mechanics; the JKR method

• Heterogeneous nucleation

• Processes based on wettability changes or differences
  • Detergency
  • Flotation
  • Selective or “spherical” agglomeration
  • Offset lithographic printing

• Wicking flows (capillary action) and absorbency
  • Wicking into a single capillary tube
  • Wicking in porous media
  • Practical strategies for promoting absorbency
  • Immiscible displacement
  • Mercury porosimitry
  • Motion of liquid threads
  • Surface wicking; spreading over rough or porous surfaces

• Particles at interfaces
  • Particles at solid-fluid interfaces: effects on wetting and spreading
  • The disposition of particles at fluid interfaces
  • Particle-assisted wetting
  • Pickering emulsions
  • Armored bubbles and liquid marbles
  • Janus particles and nanoparticles at fluid interfaces

• The description of solid surfaces
  • Solid surface roughness
  • Fractal surfaces
  • Surface texture
  • Measurement of surface roughness and texture by stylus profilometry

• Optical techniques for surface characterization
  • Optical microscopy
  • Optical profilometry
  • Confocal microscopy
  • Electron microscopy
  • Near-field scanning optical microscopy (NSOM)

• Scanning probe microscopy (SPM)
  • Scanning Tunneling Microscopy (STM)
  • Atomic Force Microscopy (AFM)

• Surface area of powders, pore size distribution

• Energetic characterization of solid surfaces: Inverse Gas Chromatography (IGC)

• Some fun things to do: Experiments and demonstrations for Chapter 4
  • Contact angles
  • Making self-assembled monolayers (SAM's), and measuring their wettability
  • Use of a superspreader
  • Contact adhesion
  • Playing with Magic Sand®
  • Liquid marbles
  • Wicking of water into filter paper
  • Capillary rise in a narrow groove

The following sections are included:

• Preliminaries
  • Definition and classification of colloids
  • General properties of colloidal dispersions
  • Dense vs. dilute dispersions

• Mechanisms of lyophobic colloid instability
  • Phase segregation: the “phoretic processes”
  • Thermodynamic criteria for stability
  • Aggregation
  • Coalescence
  • Particle size disproportionation

• Preparation of colloid particles and colloidal dispersions
  • Classification of preparation strategies for lyophobic colloids
  • Top-down strategies
  • Bottom-up strategies

• Morphology of colloids: particle size, size distribution, and particle shape
  • Description of particle size distributions
  • Distributions based on different size variables and weighting factors
  • Normal (Gaussian) and log-normal (log-Gaussian) distributions
  • Particle shape

• Sedimentation and centrifugation
  • Individual particle settling: Stokes' Law
  • Multi-particle, wall and charge effects on sedimentation
  • Differential sedimentation; particle size analysis
  • Centrifugation

• Brownian motion; sedimentation-diffusion equilibrium
  • Kinetic theory and diffusion
  • Brownian motion
  • Sedimentation (centrifugation) – diffusion equilibrium
  • Practical retrospective regarding sedimentation and other phoretic processes

• Measurement of particle size and size distribution: overview
  • Classification of methods
  • Microscopy

• Light scattering
  • Classical (static) light scattering
  • Rayleigh scattering
  • Turbidity
  • Rayleigh-Gans-Debye (RGD) scattering
  • Mie scattering
  • Fraunhofer diffraction; laser diffraction
  • Inelastic scattering: absorbance; the Raman effect
  • Scattering from denser dispersions
  • Dynamic Light Scattering (Photon Correlation Spectroscopy)
  • Dynamic light scattering from denser dispersions

• Aperture, chromatographic and acoustic methods for particle sizing
  • Aperture (one-at-a-time) methods
  • Chromatographic methods
  • Acoustic methods

• Some fun things to do: Experiments and demonstrations for Chapter 5
  • Synthesis of a colloid of sulfur particles in water and its interaction with light
  • Synthesis of monodisperse silica particles via the Stöber process
  • Sedimentation of a monodisperse colloid

The following sections are included:

• Origin of charge separation at interfaces
  • Overview
  • Preferential adsorption/desorption of lattice ions
  • Specific adsorption of charged species
  • Ionization of surface functional groups
  • Isomorphic substitution
  • Accumulation/depletion of electrons
  • Interface charging in non-aqueous systems

• Electric double layer formation and structure
  • The Helmholtz model; electrostatic units
  • The Gouy-Chapman model; Poisson-Boltzmann equation
  • Boundary conditions to the Poisson-Boltzmann equation
  • Double layers at spherical and cylindrical surfaces
  • The free energy of double layer formation
  • The Stern model; structure of the inner part of the double layer
  • The mercury solution interface; electrocapillarity and refinements to the double layer model
  • Oriented dipoles at the interface: the x-potential

• Electrostatic characterization of colloids by titration methods
  • Colloid titrations
  • Potentiometric titrations
  • Conductometric titrations
  • Donnan equilibrium and the suspension effect

• Electrokinetics
  • The electrokinetic phenomena
  • The zeta potential and its interpretation
  • Electrokinetic measurements; micro-electrophoresis
  • Relationship of zeta potential to electrophoretic mobility
  • Electrokinetic titrations
  • Electro-acoustic measurements

• Dielectrophoresis and optical trapping
  • Dielectrophoresis
  • Electrorotation and traveling wave dielectrophoresis
  • Optical trapping; laser tweezers

• Some fun things to do: Experiments and demonstrations for Chapter 6
  • Electrophoresis of an electrocratic colloid
  • Streaming potential

The following sections are included:

• Overview and rationale

• Long-range van der Waals interactions
  • The Hamaker (microscopic) approach
  • Retardation
  • The Lifshitz (macroscopic) approach
  • Measurement of Hamaker constants

• Electrostatic interactions; DLVO theory
  • Electrostatic repulsion between charged flat plates
  • Electrostatic interactions between curved surfaces; the Derjaguin approximation
  • DLVO theory: electrocratic dispersions
  • Jar testing, the Schulze-Hardy Rule and agreement with theory
  • The Hofmeister series; ion speciation and ionic specific adsorption
  • Repeptization
  • Interaction between dissimilar surfaces: hetero-aggregation

• Kinetics of aggregation
  • Classification of aggregation rate processes and nomenclature
  • Smoluchowski theory of diffusion-limited (rapid) aggregation
  • The hydrodynamic drainage effect
  • Orthokinetic (shear flow induced) aggregation
  • Reaction-limited (slow) aggregation; the stability ratio W
  • Secondary minimum effects
  • Kinetics of hetero-aggregation
  • Measurement of early-stage aggregation kinetics (W)
  • Surface aggregation
  • Electrostatic stabilization and aggregation rates in apolar media

• Steric stabilization and other colloid-polymer interactions
  • Polymer adsorption and steric stabilization
  • Thermodynamic considerations: enthalpic vs. entropic effects
  • Fischer theory
  • Steric repulsion plotted on DLVO coordinates
  • Electro-steric stabilization
  • Bridging flocculation
  • Depletion flocculation
  • Electrophoretic displays; electronic paper

• The kinetics (and thermodynamics) of flocculation

• Other non-DLVO interaction forces

• Aggregate structure evolution; fractal aggregates
  • Stages of the aggregation process
  • Fractal aggregates
  • The effect of particle size on aggregation phenomena; coating by nanoparticles

• Some fun things to do: Experiments and demonstrations for Chapter 7
  • Determination of the Critical Coagulation Concentration (CCC) by jar testing
  • Formation of a colloidal gel
  • Destruction of a colloidal gel

The following sections are included:

• Rheology: scope and definitions

• Viscometry
  • Newton's Law of viscosity
  • Measurement of viscosity

• The viscosity of colloidal dispersions
  • Dilute dispersions; Einstein theory
  • Denser dispersions of non-interacting particles
  • Dilute dispersions of non-spherical particles

• Non-Newtonian rheology
  • General viscous behavior of dispersions of non-interacting particulates
  • Fluids with a yield stress
  • Time-dependent rheology
  • Viscoelasticity

• Electroviscous effects

• Some fun things to do: Experiments and demonstrations for Chapter 8
  • Dilatant behavior in a bottle
  • Yield stress of a colloidal gel

The following sections are included:

• General consideration of emulsions
  • Classification of emulsions
  • Emulsifiers and emulsion stability
  • Thermodynamics of emulsification/breakdown
  • Preparation of emulsions

• O/W or W/O emulsions?
  • Rules of thumb
  • The hydrophile-lipophile balance (HLB) and related scales
  • Double (or multiple) emulsions

• Application of emulsions
  • Formation/breaking in situ
  • Demulsification

• Microemulsions
  • Distinction between microemulsions and macro emulsions
  • Phase behavior of microemulsion systems
  • Ultra-low interfacial tension
  • Interfacial film properties in microemulsion systems

• General consideration of foams
  • Nature and preparation of foams
  • Stages in foam lifetime
  • Stability mechanisms
  • Foam behavior and foaming agents
  • Antifoam action
  • Froth flotation
  • Foaming in non-aqueous media; general surface activity near a phase split

• Some fun things to do: Experiments and demonstrations for Chapter 9
  • Making, testing and breaking macro emulsions
  • Making a microemulsion
  • Making and breaking foams

The following sections are included:

• Unbalanced forces at fluid interfaces
  • Unbalanced normal forces
  • Tangential force imbalances: the Marangoni effect
  • Boundary conditions at a fluid interface

• Examples of Interfacial Hydrodynamic Flows
  • The breakup of capillary jets
  • Steady thermocapillary flow
  • The motion of bubbles or drops in a temperature gradient
  • Marangoni instability in a shallow liquid pool – Bénard cells

• Some Practical Implications of the Marangoni Effect
  • Marangoni effects on mass transfer
  • Marangoni drying
  • Marangoni patterning

• The Effect of Surface Active Agents
  • Gibbs elasticity
  • The boundary conditions describing the effects of surfactants
  • The effect of surfactants on bubble or droplet circulation
  • The effect of surfactants on the stability of a pool heated from below

• Some fun things to do: Experiments and demonstrations for Chapter 10
  • Tears of strong wine
  • Thermocapillary flow
  • Bénard cells
  • Jet breakup
  • Marangoni effects in foam films and puddles

The following sections are included:

• Appendix 1

• Appendix 2

• Appendix 3

• Index